A device for the automatic replacement of the tools in a bending machine

Abstract: A device for the automatic replacement of the tools (punches and dies) in a bending machine comprises a movable structure (380) carrying a tool-gripping head (382), which is movable along three perpendicular axes between a tool store and the bending machine, the gripping head (382) having rapid engagement means for gripping at least one punch-die pair (84, 86) in the attitude in which the tools are mounted on the machine.

Description: Technical Field The present invention relates to the production of bent sheet-metal articles and concerns a device for the automatic replacement of the tools in a bending machine of the kind defined in the preamble of claim 1. Background Art Known pedestal robots of the type comprising an arm with upper and lower jointed sections and a gripper hand are suitable devices for the automatic replacement of the tools in a bending machine as defined in the preamble of claim 1. The invention has been developed to solve the problem of the bending of sheet-metal articles of complex shapes which are frequently used in machines such as photocopiers, facsimile machines and various electronic devices. These products are subject to rapid development and manufacturers therefore often change models from one year to another. Each new model is the product of a redesign, even as regards the various sheet-metal articles which it contains. These bent sheet-metal articles are therefore produced on a relatively small scale and thus do not justify complex and expensive tools and dies. A system for producing bent sheet-metal articles known from document US-A-4 991 422 departs radically from previously existing bending systems which use bending presses with fixed frameworks and linear, V-sectioned punches and dies which are movable vertically towards and away from each other. The system described in US-A-4 991 422 provides for a piece which is to be bent to be supported by a manipulator so that a region of the piece which is to be bent lies in a vertical suspension plane. The bends are effected by means of an oscillating bending machine having two tools which can be disposed in any configuration relative to the piece to be bent. The piece is supported by the manipulator in a manner such that it can perform movements of limited extent with five degrees of freedom, excluding rotation about an axis perpendicular to the plane of the undeformed piece of sheet metal. The bending machine also has a device for the rapid replacement of the tools, using two rotary turrets carried at the ends of a C-shaped tool-holder structure. Disclosure of the Invention The object of the present invention is further to develop a device for the replacement of the bending tools which constitutes an improvement to that disclosed in US-A-4 991 422. This object is achieved by means of a device having, essentially, the characteristics defined in the claims. Brief Description of the Drawings The present invention will now be described in detail with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic, perspective view showing a system which includes a device according to the invention, Figure 2 is a schematic, perspective view of the bending machine indicated by the arrow II in Figure 1, Figure 3 is a detail of the part indicated by the arrow III in Figure 2, Figures 4 and 5 are sections taken on the line IV-IV of Figure 3, showing the device for the rapid engagement of the tools. Figures 6-14 show the tool-gripping head, indicated by the arrow VI in Figure 1, of a device for automatically replacing the tools of a bending machine and, more precisely, Figure 6 is a schematic, perspective view of the gripping head, Figure 7 is a partially-sectioned side view of the gripping head, Figure 8 is a view taken on the arrow VIII of Figure 7, Figure 9 is a partial view of the tool store, from above, taken on the arrow IX of Figure 1, Figure 10 is a section taken on the line X of Figure 8, on an enlarged scale, and Figures 11, 12, 13 and 14 are schematic views showing the sequence for replacing a pair of tools of the bending machine. Best Mode for Carrying out the Invention A system for producing bent sheet-metal articles and the devices making up the system will now be described with reference to the drawings. The system for producing sheet-metal articles With reference to Figure 1, a system for producing bent sheet-metal articles from blanked or laser-cut pieces of sheet metal of shapes corresponding to the development in a plane of the articles to be produced, is generally indicated 50. The system 50 comprises a station 52, for positioning the pieces of sheet metal, a measurement and storage station 54, a bending station 56, an output station 58 and a device 60 for the automatic replacement of the tools, with a respective tool store 62. The bending station 56 comprises a cartesian manipulator 64 including a vertically-movable device 66 carried by a carriage 68 movable along a beam 70 which in turn is movable along guides 72 of a portal structure 74. The movable device 66 of the manipulator 64 carries a suspension head 76 which will be described in detail below, for holding vertically, by means of a gripper, a piece of sheet-metal to be bent. The suspension head 76 of the manipulator 64 supports the piece in a manner such that it floats freely, so that the piece is free to perform movements of a limited extent during bending. In order to execute each bend, the manipulator 64, which is controlled by a conventional control unit 78, positions the piece in a position which is determined on the basis of a program established in dependence on the geometrical shape of the piece to be worked. The bending station 56 also comprises a bending machine 80 comprising a tool-holder structure 82 having a punch 84 and a die 86 which cooperate with each other. As will be described in detail below, the tool-holder structure 82 is rotatable about an axis which passes through the bending line defined by the vertex of the V-shaped punch 84 and can also pivot about a horizontal axis perpendicular to the aforesaid axis of rotation. It will therefore be appreciated that the punch 84 and the die 86 can be disposed in any position relative to the piece to be bent. The rotary and pivoting movements of the tool-holder tructure 82 are brought about by the control unit 78 on the basis of a predetermined program. It is important to underline that the precision of the positioning of the piece in space, like the precision of the positioning of the tools, is of decisive importance since, unlike conventional bending methods, there are neither mechanical abutments to define the position of the piece nor systems for measuring the position of the piece relative to the bending machine. The necessary precision in the positioning of the piece is achieved by virtue of a preliminary determination of the relative piece-manipulator position and of the precise control of the relative manipulator-bending machine positions, which is achieved by virtue of the operating precision of the manipulator 64 and of the bending machine 80. The operating principle upon which the bending system of Figure 1 is based thus consists of the positioning of a piece of sheet metal in a predetermined region in space with great precision and repeatability, and of the modification of the positions of the bending tools relative to the piece, with a corresponding degree of precision and repeatability, by a movement of the bending machine, so as to execute the bend in the desired region. For further clarification as regards the operating principle of the system according to the present invention, reference should be made to US-A-4 991 422. The main characteristic of the system according to Figure 1 is its ability to work on extremely small batches (even a single piece) of pieces with different geometrical shapes, solely by means of the selection of a different working program, without carrying out tooling operations. A first problem which had to be solved in order to achieve a high degree of flexibility of the system was that of devising a unit for loading the pieces which enabled shaped pieces of sheet metal of complex shapes and extremely variable dimensions to be stored and subsequently gripped by the suspension head 76 of the manipulator 64. With conventional grippers carried by the head of the manipulator, in addition to the difficulty of producing a universal gripper which can grip pieces of different geometrical shapes, there is the problem of the precise positioning of the piece relative to the gripper and hence relative to the locating system of the manipulator, that is, the problem of how to position the piece precisely on a loading device which, at the same time, can be adapted to pieces which differ greatly in shape and size. In the system according to Figure 1, these problems have been overcome by virtue of the fact that each piece is associated with its own gripper which is fitted on to a predetermined region of the undeformed piece of sheet metal. The gripper is fitted on to the piece of sheet metal in the positioning station 52. The pieces, with their respective grippers, are disposed in a store 90 to await transfer to the bending station 56. The store 90 can easily house pieces of different geometrical shapes without the need for any tooling, by virtue of the use of the gripper. In fact, the store 90 can accommodate a certain number of grippers which are inserted in a corresponding number of forks forming part of the store. The pieces of sheet metal, each gripped by its own gripper, are disposed vertically, suspended by the gripper itself, and thus have no direct connection with the store 90 which is completely independent of the shapes of the sheets. After each piece of sheet metal has been provided with its gripper, the piece is subjected to a measurement step carried out by means of a conventional feeler 88. The data detected by this measurement are processed and stored by the control unit 78 which establishes the link which exists between a locating system fixed relative to the piece and a locating system which is fixed relative to the gripper and, consequently, is fixed relative to the suspension head 76 of the manipulator 64. Small corrections can thus be made to the program controlling the manipulator 64 to compensate for errors in the positioning of the piece relative to the gripper. The piece may be measured when it is already connected to the suspension head 76 of the manipulator 64. In this case, the feeler 88 must be movable in order to enter and leave the working area. If the cycle for the working of the piece provides for the gripping region to be changed after some bends have been effected, a new measurement can be made after the piece has been gripped in the new position. Alternatively, and as shown in Figure 1, the measurement may be effected outside the working area, without affecting the time taken by the bending cycle, whilst the piece is supported by an auxiliary manipulator 89. The device 60 for replacing the tools of the bending machine 80 is constituted by a cartesian robot having a carriage 94 movable on a beam 96 which in turn is movable on the guides 72 of the portal structure 74. The characteristics of the tool-gripping head of the device for the automatic replacement of the tools, as well as the method for the automatic replacement of one or both of the tools of the bending machine 80 are described below. The bending machine With reference to Figure 2 in particular, the bending machine 80 comprises a fixed base 280 carrying a cradle 282 which is pivotable relative to the fixed base 280 about a horizontal axis 284. The cradle 282 is rotated about the axis 284 by a numerically-controlled motor 286. A tool-holder structure 288 is rotatably mounted on the cradle 282 by means of a thrust bearing (not shown), the axis of rotation 292 of which coincides with the bending line defined by the vertex of the V-shaped punch 84. The tool-holder structure 288 is rotated about the bending line 292 by a numerically-controlled motor 294. The rotations of the tool-holder structure 288 about the axes 292 and 284 enable the punch-die unit to be placed in any position relative to the piece to be bent. Moreover, during the execution of each bend, the punch-die unit moves under the control of a predetermined program, following the natural movement of the flange of the piece due to the bending action. For a detailed description of the operation principle of the bending machine 80, reference should be made to the US-A-4 991 422 already mentioned above. The device for the rapid engagement of the bending tools on the tool-holder structure 288 will now be described with reference to Figures 3, 4 and 5. Only the device for rapid engagement between the die and the slide 310 will be described since the rapid engagement device for the punch is identical thereto, with the sole difference that the engagement device is disposed in the pivoting support 300 instead of in the body of the slide 310. With reference to Figures 4 and 5, which are sections taken on the line IV-IV of Figure 3, on an enlarged scale, a piston, indicated 344, is movable in a chamber 346 in which two regions 348 and 350 for supply with pressurized fluid are defined and are supplied in order to bring about the release and the engagement of the die 86, respectively. An engagement tooth 352 having a wedge-shaped surface 354 is fixed rigidly to the piston 344. The slide 310 has a plate 356 with flat bearing surfaces 358 against which corresponding surfaces 360 of the die 86 bear. A hole with a locating surface 372 is formed in the plate 356. The die 86 has a shank 362 having a locating surface 364 and a recess 366 with an inclined surface 368 for cooperating with the wedge-shaped surface 354 of the engagement tooth 352. A helical compression spring 370 interposed between the piston 344 and an internal end wall of the cavity 346 urges the piston 344 towards the engagement position shown in Figure 5. Starting from the configuration of Figure 4, in order to engage the die 86, pressurized fluid is sent to the supply region 348 so as to move the piston 344 against the action of the spring 370. The displacement of the engagement tooth 352 creates a space for the insertion of the shank 362 in the hole in the plate 356. The supply of fluid to the region 348 is then cut off but the region 350 is supplied, thus generating a force which is added to that generated by the spring 370, causing the piston 344 to move in the direction indicated by the arrow 374 in Figure 5. The purpose of the spring 370 is to ensure that the tool 86 remains connected to the portion 312 even if the supply of pressurized fluid to the region 350 should accidentally fail. The inclined surfaces 368 and 354 generate an oblique engagement force having a component parallel to the bending plane which keeps the flat surfaces 360 of the die 86 in contact with the flat surfaces 358 of the plate 356. The engagement force also has a component perpendicular to the bending plane which keeps the locating surface 364 in contact with the corresponding locating surface 372 of the plate 356. This enables precise and highly repeatable positioning of the bending tools relative to the slide 310 and relative to the pivoting support 300. The device for the automatic replacement of the bending tools As has been seen in the general description of the system, the replacement of one or both the tools of the bending machine is effected by means of an automatic tool-changing device constituted by a cartesian robot which can move freely between a tool store and the bending machine. The tool-gripping head of the tool-changing robot and the method followed in order to replace the tools of the bending machine will now be described with reference to Figures 6 to 14. With reference initially to Figures 6 to 8, the movable device of the tool-changing robot is indicated 380 and carries a head 382 for gripping the tools. As can be seen in Figure 7, the head 382 is connected to the movable device 380 by means of a plurality of resilient elements constituted by blocks 384 of elastomeric material which allow the head 382 limited freedom to float relative to the movable device of the robot. A clamping device, schematically indicated 386, has three movable clamping members 388, only one of which is visible in the drawing, and which are intended to clamp the head 382 with respect to its freedom to float. The clamping members 388 engage respective seats 389 in an element 391 fixed to a plate 390 (Fig. 6) of the head 382. The resilient suspension system of the head 382 is useful during the tool-changing sequence to compensate for any errors in the relative positioning of the robot and the bending machine, and the suspension can be clamped during the highspeed movements of the robot, to prevent oscillations of the head. As can be seen in Figure 6 in particular, the gripping head 382 comprises the plate 390 carrying three pairs of gripping fingers 392, 394 and 396 which are fixed relative to the plate 390 and between which two pairs of seats 400 and 402 are defined for housing two pairs of bending tools, each constituted by a punch and a die. As can be seen in Figure 9, the bending tools are arranged in punch-die pairs, each contained in a vertical plane, in a storage structure with a rack, schematically indicated 406. Each punch-die pair is sufficiently spaced from the adjacent pair to allow a pair of gripping fingers to be inserted between them, as shown schematically in Figure 9. With reference to Figures 7 and 8, each of the gripping fingers 394 and 396 comprises a device for engaging the tools, comprising a pair of pistons 408 with rounded heads, each of which has a wedge-shaped surface 410 cooperating with a corresponding wedge-shaped surface 412 of a slidable operating rod 414. The two rods 414 of each gripping finger are operated by a single actuator 416 by means of a pivoting plate 418. A downward movement of the rods 414 causes the ends of the pistons 408 to emerge and engage corresponding recesses 420 in a base portion 422 of the bending tool. The base portion 422 is thus pressed against the surface 424 of the opposite gripping finger (Figure 8). As can be seen in the detail of Figure 10, each piston 408 is associated with a biasing spring 426 which, as a result of the raising of the rod 414, causes the piston 408 to reenter the gripping finger 394 so as to release the base portion 422 of the tool. The fact that the punch and the die are gripped between two pairs of gripping fingers enables the two tools to be kept in the same configuration in which they are mounted on the bending machine, which greatly simplifies tool-replacement operations. The sequence for the replacement of the tools in the bending machine will now be described with reference to Figures 11 to 14. The portions of the bending machine which are movable towards each other are indicated 430 and 432 and a first pair of tools which is connected to the two portions 430, 432 of the bending press initially is indicated 434. A pair of replacement tools is indicated 436. The tool-changing robot is first brought near to the tool-holding store and picks up a pair of replacement tools 436, extracting them from the rack structure 406 from above after it has gripped them between two pairs of gripping fingers 394, 396. This step is normally carried out whilst the bending machine is carrying out its normal bending cycle with the tools 434. In order to replace the tools, the bending machine is brought to a configuration in which the bending plane extends vertically and in which the punch and the die are in contact with each other (Figure 11). The gripping head of the tool-changing robot is made to descend from above so as to position the first pair of tools 434 between the gripping fingers 392, 394, as shown in Figure 11. After the tools 434 have been gripped by means of the engagement devices described above, the rapid engagement means which connect the tools 434 to the two portions 430, 432 of the bending press are released. The two portions 430, 432 are then moved apart, as shown in Figure 12, releasing the first pair of tools 434. This is achieved by means of a displacement of the movable part 430 by a distance 2A in the direction indicated by the arrow 438 in Figure 12, together with a displacement of the tool-holder head by a distance A in the same direction. The tool-holder head is then moved until the pair of replacement tools 436 is brought into correspondence with the rapid engagement devices of the bending machine (Figure 13). Finally, the portions 430 and 432 of the bending machine are brought together again and the rapid engagement devices are activated and connect the replacement tools 436 to the tool-holder structure of the bending machine. When the engagement of the replacement tools 436 on the tool-holder structure has been completed, the engagement means of the gripping fingers 394 and 396 are disengaged. The sequence described may also be carried out in a slightly modified form to replace only one of the bending tools (generally the punch). The fact that the tool-changing robot 60 is independent of the manipulator 64 for the pieces of sheet metal and of the bending machine 80 enables the tool store 62 to be equipped simultaneously with the normal working cycle of the system. In Figure 1, an interface position, indicated 440, is disposed within the reach of the tool-changing robot and can be reached by an operator without danger of being struck by moving parts. The operator places the tools in the interface position 440 and removes them therefrom without interrupting the working cycle of the system and the tool-changing robot takes the tools from the interface position and positions them in the store 62. The robot also places the tools which are not used in a certain bending cycle in the interface position, so as to leave space free in the store 62 for the tools actually being used.

Claims: A device for the automatic replacement of the tools in a bending machine comprising a punch (84) and a die (86) connected to a tool-holder structure (288) by rapid attachment means, a movable structure (380) carrying a tool-gripping head (382), which is movable along three perpendicular axes between a tool store and the bending machine, the gripping head (382) having rapid attachment means for gripping at least one punch-die pair (84, 86) in the attitude in which the tools are mounted on the machine, characterized in that it comprises a clamping device (386, 388) which connects the gripping head (382) to an end portion (380) of the movable structure and disconnects it therefrom, a resilient connecting element (384) also being provided for connecting the tool-gripping head (382) to the movable structure resiliently when the clamping device is disengaged. A device according to Claim 1, characterized in that the gripping head (382) comprises two independent pairs of gripping elements for simultaneously gripping a replacement pair of tools (436) and a pair of tools (434) which has been removed from the bending machine (80). A device according to Claim 1, characterized in that the gripping head comprises three parallel pairs of fingers (392, 394, 396) between which two pairs of seats (400, 402) are defined for respective pairs of tools, at least two pairs of fingers (394, 396) having gripping devices each comprising at least one piston (408) which can slide transverse the respective finger between a projecting position and a retracted position and a wedge-shaped element (410, 414) which is movable parallel to the finger in order to cause the cylinder to emerge so as to grip the tool against a facing finger.

Inventors: SARTORIO FRANCO, SARTORIO, FRANCO
Applicants: AMADA CO LTD, CREA SRL, AMADA COMPANY, LIMITED, CREA S.R.L.
Application year: 1994
Main classification: B21D37
IPC codes: B21D37, B21D43, B21D5, B21D11